Proposed: .270 Marlin Express Rifle Cartridge
The creative geniuses at Hornady, in developing their line of Evolution (EVO) flex-tip spitzer bullets, have opened a whole world of new possibilities for traditional lever action rifles. Or, for that matter, any rifle designed to be fed from a tubular magazine (pump, autoloader, whatever).
Flex-Tip bullets were first applied to the .30-30 Winchester and then in quick succession added to the .35 Remington, .444 Marlin, .45-70 and .32 Win. Special. The latest and greatest factory offering for lever action rifle fans from Hornady is the .308 Marlin Express cartridge with, of course, an EVO bullet that allows it to deliver near-.308 Winchester performance from the 24" barrel of a Marlin 336XLR rifle.
Not being as creative as the folks at Hornady, we here at Guns and Shooting Online did not anticipate the possibility of a cartridge like the .308 Marlin, which combines an EVO bullet with the latest in non-canister designer powders to achieve its high level of performance at moderate pressure from a .30-30 length case. We can, however, jump on a bandwagon with the best of them!
To prove it, during the winter of 2007 we proposed a new .338 cartridge based on the .308 Marlin case. We called our new wildcat the ".338 Marlin Express." It was conceived not to duplicate the ballistics of any previous cartridge, but to offer the ballistics and advantages of the .338x57 O'Connor wildcat to modern lever action rifle shooters. (You can read about the .338 Marlin Express on the Rifle Information, Wildcat Cartridge ane Rifle Cartridge pages.) We forwarded that proposal to our friends at both Marlin and Hornady, who ultimately developed their own version on a brand new case.
The latest Guns and Shooting Online idea for a new cartridge to take advantage of Hornady EVO technology came about during an exchange of e-mails with Anthony Imperato, the President of Henry Repeating Arms. To wit, neck down the .308 Marlin Express case to accept a .270 (.277" diameter) 130 grain EVO spitzer bullet, which at this writing does not exist. This one we'll call the .270 Marlin Express, hoping that either Marlin or Henry (or someone) will step up and partner with Hornady to get it done.
Certainly, as soon as .308 Marlin Express cases become available to reloaders, wildcatters will begin necking the case up and down. Among the most obvious are calibers .338, .257, .270, 7mm and .35.
There has long been a demand for a flat shooting, sub-.30 caliber cartridge for use in lever action rifles. The .250 Savage was a successful cartridge while Savage Model 99 rifles were popular and the .270 Savage was a popular wildcat. The 7-30 Waters (a .30-30 case necked down to accept .284" bullets) even reached production status when Federal started offering factory loaded ammunition (a 120 grain FP bullet at a MV of 2700 fps). For a while Winchester offered Model 94 rifles in the caliber. However, the 7-30 Waters was not a big success because of the limitations of the flat point bullet required by the Model 94's tubular magazine. It simply could not maintain enough of its velocity downrange to offer sufficient improvement over the .30-30.
Hornady's development of the Flex-Tip Evolution bullet has changed the rules of the game. Now, spitzer bullets with reasonable ballistic coefficients (BC) can be designed for rifles with tubular magazines. New cartridges designed for traditional lever action rifles can offer near bolt action cartridge performance if an EVO spitzer bullet is made available for them. The 160 grain EVO .30-30 bullet, for example, has a BC of .310 and the new 160 grain EVO bullet for the .308 Marlin Express has a BC of .400. Compare that to the .196 BC of Hornady's 139 grain FP bullet for the 7-30 Waters!
A 130 grain .270 (.277") bullet has very nearly the same sectional density (.242) as a 160 grain .308" bullet (SD .241). Sectional density (SD) plus form determine BC, so it should be possible to design a new EVO bullet for our proposed .270 Marlin Express cartridge with a BC in the vicinity of .400 for a necked-down .308 Marlin Express case.
I can see no reason to change the .308 Marlin's case length, diameter, or cartridge overall length for the new .270 Marlin Express. I suppose we could use the new and slightly larger .338 Marlin Express case as the basis for our proposed .270 Express, but the fatter body and smaller rim of the .338 case do not feed as smoothly in the 336 action as the .308 Marlin case. Hornady designers carefully determined the parameters of the .308 Marlin case for a bullet of nearly identical length and shape as our 130 grain .270 bullet, so let's just assume that they knew what they were doing and go with it.
Here are some proposed cartridge dimensions for the .270 Marlin Express: .506" rim diameter, .063" rim thickness, .4703" base diameter, .455" shoulder diameter and .308" neck diameter. The case length should be pegged at 1.920" with a body length from the base of the rim to the beginning of the shoulder of 1.460" and a 20 degree shoulder angle. Given those dimensions the neck should turn out to be about one caliber long. If a longer neck is deemed necessary, the shoulder angle could be sharpened to 25 degrees. The maximum overall cartridge length is 2.60". The Maximum Average Pressure (MAP) of the new cartridge is likely to be in the vicinity of 47,500 cup.
What kind of ballistics can we expect from the .270 Marlin Express? I would expect a velocity gain of 100 fps or more compared to the 160 grain .308 Marlin EVO load. Since that cartridge has a factory loaded MV of 2660 fps, a MV of 2760-2800 fps should not be unreasonable for the .270 Express.
Here are the expected velocity/energy figures from the muzzle to 300 yards for a 130 grain EVO bullet (SD .242, BC .400): 2800 fps/2263 ft. lbs. at muzzle, 2576 fps/1915 ft. lbs. at 100 yards, 2363 fps/1612 ft. lbs. at 200 yards, and 2162 fps/1349 ft. lbs. at 300 yards. Those should be pretty exciting numbers for the fan of traditional lever action rifles.
The trajectory of that load should look like this when zeroed to take advantage of its maximum point blank range (MPBR) +/- 3" for a rifle with a scope sight mounted 1.5" overbore: -1.5" at muzzle, +2.7" at 100 yards, +1.6" at 200 yards, -5.7" at 300 yards. The MPBR of that load is 273 yards. That compares favorably to the .308 Marlin, which has a MPBR (+/- 3") of 261 yards.
The recoil energy of the .270 Express should be around 11.5 ft. lbs., which is markedly less than the estimated 14 ft. lbs. of the .308 Marlin Express in a scoped rifle weighing 8 pounds--the approximate weight of a scoped Marlin 336XLR.
In killing power, the .270 Marlin Express should be suitable for all CXP2 game including caribou and black bear within 250 yards and adequate for mule deer, mountain goats, big horn sheep and pronghorn antelope to beyond 300 yards. It should be very similar to the .260 Remington, 6.5x55 and 7x57 at all ranges from the muzzle to 300 yards and beyond, given bullets with a BC of around .400 in all three cartridges, and clearly superior to the 6.8mm Rem. SPC. There can be no question about the effectiveness of hunting cartridges in this general class, as they have been used successfully around the world for over 100 years.
No doubt the advent of the .270 Marlin Express, should it be commercially adopted, would spark another .270 vs. .30 caliber debate, this time among lever gun fans. Predictably, those who favor higher velocity will choose the .270 Marlin Express and those who favor heavier bullets will champion the .308 Marlin Express. That is okay, too, as we gun writers always need something to write about! Now what lever action rifle fans need is for some manufacturer to partner with Hornady and step up to the plate to make the .270 Marlin Express a reality.
Note: This article is mirrored on the Wildcat Cartridges page.
Copyright 2007, 2012 by Chuck Hawks. All rights reserved.